1. Field of the Invention
The present invention relates to a driving device for, for example, a sheet processing apparatus for diagonally feeding and shift-loading a sheet to be carried in either of the sheet width directions.
2. Description of the Related Art
As a finishing process apparatus connected to a copy machine or other image forming apparatus, a sheet processing apparatus has been proposed (Japanese Patent Laid-Open No. 2002-193537) in which, a sheet being carried by a diagonal feed mechanism disposed along a sheet carrying path is diagonally fed towards the front (near side) of the apparatus or towards the rear (back side) of the apparatus, that is, in the sheet width direction intersecting the sheet carrying direction at a right angle, and is shift-loaded (shifted and loaded) according to the width of the sheet.
This diagonal feed mechanism comprises two diagonal feed roller pairs positioned separated from each other in the sheet width direction intersecting with the carrying direction of the sheet at a right angle. The two diagonal feed roller pairs are positioned diagonally such that the respective axes thereof intersect downstream along the sheet carrying direction.
Depending on the shift direction of the sheet, rollers of one of the diagonal feed roller pairs are caused to close and sandwich and carry the sheet while rollers of the other diagonal feed roller pair are caused to open, thus diagonally feeding the sheet towards the front or towards the rear of the apparatus. The action of the rollers of the two diagonal feed roller pairs closing and opening is controlled by a driving unit (such as a pulse motor, etc.).
Incidentally, when powering up, the positions of the rollers in the direction of closing and opening of the diagonal feed roller pairs is undetermined. For this reason, in order to determine accurately the initial position of the diagonal feed rollers, generally the diagonal feed rollers provided with a detection flag are moved and the position of the diagonal feed rollers is detected by sensors, the initial position of the diagonal feed rollers thus being determined accurately based on these detection results.
However, in this case position sensors must be provided for each of the two diagonal feed roller pairs, incurring a cost.
Accordingly, in Japanese Patent Laid-Open No. 2002-193537 mentioned above, an abutting member is provided to the diagonal feed roller that is movable, and this diagonal feed roller is moved during initialization towards a positioning member which is immovably fixed, and the abutting member abuts the positioning member, thus determining the initial position of the diagonal feed rollers. It is thus possible to determine accurately the initial position of the diagonal feed rollers without using position sensors, making it possible to cut costs.
However, with the above prior art, if the abutting member of the diagonal feed roller is already abutting the positioning member when powering up, a motor is driven so as to move the movable diagonal feed roller towards the positioning member with the abutting member already abutting the positioning member. This causes the problems of the motor losing synchronization, a reduction in quietness, and a reduction in the durability of the diagonal feed mechanism due to a large load.